The present invention relates to systems and method reforming bulge testing of thin films and coatings of the type used in the semiconductor and optical industries, in the manufacture of microelectricalmechanical systems (MEMS), and in other contexts, and in particular to a chuck for supporting a substrate being tested and a method of using the chuck.
Thin films are used in a de array of products, including integrated circuit devices, optical coatings, storage media, LCD matrix arrays, cutting tools, wear-resistant coatings, sensor arrays, and MEMS. The terms xe2x80x9cthin filmxe2x80x9d and xe2x80x9cfilmxe2x80x9d are used to encompass films, coatings and layers of various thickness that are deposited on a substrate. These thickness typically range from 100 nanometers (nm)-5,000 nm, although include the range 10 nm-500,000 nm. Typically, each thin film has different residual stress characteristics and different thermal and/or mechanical properties, which may affect the performance, reliability, or durability of devices including or made using such thin films. It is often necessary to determine these materials properties in connection with research and development, manufacturing process development and control, and testing in volume manufacturing of devices including or made using thin films. Bulge testing is one technique for acquiring information concerning characteristics and properties of thin films.
Known prior art bulge systems, e.g., systems of the type described in U.S. Pat. No. 6,050,138 to Lynch et al. (xe2x80x9cthe ""138 patentxe2x80x9d), which is incorporated herein by reference, involve the use of a substrate having one or more apertures covered by the thin film to be bulge tested. Often the substrate is a silicon wafer of the type used in the manufacture of semiconductor devices, although other substrates may be used. In some cases, the apertures in the substrate are covered by a membrane or other layer of material and the thin film to be tested is deposited on such membrane or layer. The substrate is supported on a chuck and pressurized fluid, typically a gas but sometimes a liquid, is delivered via one or more orifices in the fixture to the region of the wafer where the apertures are located. The pressurized fluid causes the film, or the film and underlying membrane, to bulge, and then the materials properties may be determined as a function of the applied pressure and resultant deflection.
Existing bulge testing systems of the type described in the ""138 patent represent an important advance in the art. However, the chucks used in these systems to support the substrate suffer from an important weakness that adversely affects precise determination of the desired characteristics and properties of the thin film being tested. In particular, known bulge testers secure the substrate to the chuck using equipment and/or materials that can introduce variable and unknown stresses, that may change with time into the thin film. For example, in one embodiment of the ""138 patent, the substrate is attached to the chuck using a mounting wax, e.g., Crystal Bond(trademark) polymer available from Electron Microscopy Sciences, Fort Washington, Pa. Other embodiments of the ""138 patent involve mounting the substrate to the chuck using epoxies and cyanoacrylate adhesives and mechanical clamping techniques.
In addition to introducing variable and unknown stresses, equipment and materials of the type disclosed in the ""138 patent suffer from other problems. It tends to be difficult to quickly and easily remove the substrate from the chuck in a way that does not leave behind residues that could adversely impair the operation of the thin film. For example, as noted in the ""138 patent, when epoxies and cyanoacrylate adhesives are used, removal by heat decomposition leaves undesirable carbon residues behind. Also, dissolution of such materials in solvents such as acetone is very slow and leaves an organic residue that could alter the response of the thin film and hence impair analysis of its properties and impair further processing, such as the addition of more thin film layers or devices. While a substrate attached to a chuck with mounting wax can be removed with less difficulty than epoxies and cyanoacrylate adhesives, the removal process nevertheless takes time as it involves heating the wax until it becomes flowable. With mechanical clamping devices, as noted in the ""138 patent, it tends to be difficult to reproducibly clamp the substrate. Also, hermetic sealing of the substrate adjacent the aperture region containing the film to be tested can be difficult to achieve with mechanical systems.
One aspect of the invention is a chuck for supporting a substrate to be used in bulge testing a film using pressurized fluid provided by a source. The substrate has an aperture and a film covering the aperture. The chuck comprises a base having a first surface and a media on the first surface for contacting and inducing stiction with the substrate. The stiction is induced such that as a result of the stiction alone a force of at least 1 KPascals is required to separate a 2.54 cm by 2.54 cm square portion of a silicon wafer from the media, as measured at one of the corners of the square portion in connection with peeling the corner away from the substrate.
Another aspect of the invention a system for bulge testing a film using pressurized fluid provided by a source. The system comprises a substrate having an aperture with a film covering the aperture, a base having a first surface and a viscous media on the first surface for contacting the substrate. The viscous media creates stiction with the substrate and remains viscous at room temperature for extended periods of time.
Yet another aspect of the invention is a bulge test system for testing a portion of a film of material positioned on a substrate having an aperture positioned adjacent the film. The system comprises a source of pressurized fluid and a device for determining deflection of the film portion being bulge tested and providing a first output signal containing information representative of the extent of deflection of the film portion. In addition, the system includes a base having a first surface and a media on the first surface for contacting the substrate. The media induces stiction with the substrate such that a force of at least 1 KPascals is required to separate a 2.54 cm by 2.54 cm square portion of a silicon wafer from the media as measured at one of the four corners of the portion in connection with peeling the corner away from the substrate.
Still another aspect of the present invention is a method of bulge testing a film. The method involves providing a substrate with an aperture and a film extending over the aperture. Next, stiction is induced between the substrate and the surface such that a force of at least 1 KPascals is required to separate a 2.54 cm by 2.54 cm square portion of a silicon wafer from the media as measured at one of the corners of the portion in connection with peeling the corner away from the substrate. Then, a pressurized fluid is directed through the aperture so as to contact the film and cause it to deflect. Material properties of the film are then determined as a function of pressure of the fluid and deflection of the film.